AFFINITY-CHROMATOGRAPHY - EFFECT OF PARTICLE-SIZE ON ADSORPTION EQUILIBRIUM AND MASS-TRANSFER KINETICS

Hydrophilic and hydrophobic bonds, adsorption equilibrium, binding rates and partition and diffusion coefficients inside particles have been studied for L-asparaginase on activated Sepharose 4B with hexamethylenediamine and L(+)-chlorosuccinamic acid as the spacer arm and specific ligand, respectively, in column and batch reactors, at pH = 8.6 (borate buffer) and 298 K, for different ionic strengths (0-2.0) and different particle sizes (55-134 mum diameter). The effect of ionic strength on equilibrium was different for each particle size, being very small for larger particles (134 mum) and showing hysteresis, which was larger for small particles (55 mum). Equilibrium data were correlated using a semi-quantitative theory developed by Morrow et al. based on the Debye-Huckel theory for activity coefficients. Kinetic data at ionic strength zero were fixed using a second-order equation for adsorption and first order for desorption, the value of the adsorption constants being: k(a) = 4.4 and 7.7 g of adsorbent/mol min for particles of 55 and 66 mum and K(d) = 3.5 and 3.2 x 10(-2) min-1, respectively. 134 mum particles have internal mass transfer resistance. Thus, the partition coefficient was determined according to a model based on that of Taylor and Swaisgood, finding a value of 0.346. Also, for this size of particle, the effective diffusion coefficient was determined using the initial adsorption rate. The value of this coefficient was D(e) = 1.9 x 10(-5) cm2/s, of the same order as free diffusion for L-asparaginase.